The Clinical Epilepsy Section has been developing and testing new techniques to achieve improved seizure control, reduce drug-induced side effects, and achieve better rehabilitation in patients with severe epilepsy. These include simultaneous video and telemetered EEG recording of seizures, daily determinations of antiepileptic drug serum concentrations, and most recently, the concomitant use of positron emission tomography. Patients with very long histories of uncontrolled seizures are admitted for a complete evaluation, including all basic neurologic studies and daily objective toxicity battery. Intensive monitoring techniques are used to establish a seizure diagnosis, which is then utilized to design an appropriate therapeutic regimen for each patient. The study of positron emission tomography (PET) in patients with localized brain lesions has demonstrated focal hypometabolic cerebral areas corresponding to the interictal seizure EEG focus. In some patients, PET has been able to detect a focus when other methods have failed. Studies of patients during partial seizures have shown a change from hypo to hypermetabolism at the site of the focus. PET may also help to study the effect of seizures on cerebral metabolism beyond the limits of the epileptic focus, as well as the effect of antiepileptic drugs. Future studies using PET will also involve the Lennox-Gastaut syndrome. It is hoped that investigations of cerebral metabolism will lead to better understanding of pathophysiology and improved therapy in this severe encephalopathy of uncertain etiology. PET studies allow more definitive overall identification of the epileptic lesion and suggest new avenues of investigation into the basic mechanisms of the epilepsies. For patients who do not respond to pharmacologic therapy, the section will attempt to study noninvasive means of surgical evaluation. It is hoped that the danger of depth electrode study can be avoided by the use of PET, nuclear magnetic resonance scanning, and magnetoencephalography.